This invention relates to lubricant compositions for transmission of power, and more particularly to lubricant compositions having excellent traction coefficient and wear resistance, load carrying capacity, thermal stability, oxidation stability, rust preventing property and being effectively utilized as the lubricants for power transmission having a traction drive mechanism.
In recent years, traction drive (friction driving device utilizing rolling contact) is employed as continuously variable transmission for automobile and industrial equipment, etc. As the fluid used for the traction drive, a fluid having high traction coefficient and high power transmitting efficiency is required.
Under the circumstances, a variety of proposals are made in order to obtain fluid for traction drive having high power transmitting efficiency (for example, Japanese Patent Publications Nos. 46-338, 46-339, 47-35763, 53-36105, 58-27838, Japanese Patent Laid-open Publications Nos. 55-40726, 55-43108, 55-60596, 57-78089, 57-70895, 57-155295, 57-155296, 57-162795 and the like).
It is necessary to lubricate the traction drive mechanism with single oil since said traction drive mechanism is consisted as an apparatus for transmission of power containing gear machine, oil pressure mechanism, rolling bearings, etc. in the same system.
However, the conventional fluids for the traction drive mentioned above had improved the power transmitting efficiency, but since they were proposed exclusively for the traction drive, when used at locations such as gear mechanism, oil pressure mechanism, rolling contact bearing and the like, there are such problems as the wear resistance and load carrying capacity were not sufficient, and moreover, the thermal and oxidation stability were poor, and a large amount of sludges was generated, and they could not sufficiently withstand for practical purposes.
Under the circumstances, in order to overcome the foregoing conventional problems, blending of the additives such as extreme pressure additive, antiwear agent, antioxidant to the fluid for traction drive described in the foregoing is considered.
But, when an additive such as extreme pressure additive is merely added to the fluid for traction drive, problems such as shortening the fatigue life of the traction drive mechanism or remarkably deteriorating the power transmitting efficiency or causing corrosion, and as a result, the lubricant capable of satisfying sufficiently all the characteristics which are appropriate for practical purpose has not been available.